What is the typical sequence for a multi-pass GTAW weld on a butt joint (root, fill, cap) and the purpose of each pass?

What is the typical sequence for a multi-pass GTAW weld on a butt joint (root, fill, cap) and the purpose of each pass?

• A. Root pass shapes final contour; fill passes remove defects; cap pass establishes penetration.
• B. Root pass establishes fusion and penetration; fill passes build the weld bead to the required height; cap pass shapes the final contour and smooths the surface.
• C. Root pass only; fill and cap are optional.
• D. Root pass is for decoration only.

Answer: (B)

In a multi-pass TIG weld on a butt joint, the sequence is chosen to ensure strength, proper fill, and a clean finish. The root pass is focused on establishing fusion and penetration at the root of the joint, so the weld actually penetrates into the joint thickness and properly ties the two pieces together. Once the root is solid, the fill passes are added to build up the weld metal to the required height and width, filling the groove and shaping the bead while controlling heat input to minimize distortion and defects. The final cap pass shapes the top surface, smooths the contour, and seals the weld so it looks good and resists corrosion or environmental exposure. This order matters because without adequate root penetration the joint isn’t fully welded; without fill the weld can be underfilled; and without a dedicated cap pass the surface finish and contour would be poor.

In a multi-pass TIG weld on a butt joint, the sequence is chosen to ensure strength, proper fill, and a clean finish. The root pass is focused on establishing fusion and penetration at the root of the joint, so the weld actually penetrates into the joint thickness and properly ties the two pieces together. Once the root is solid, the fill passes are added to build up the weld metal to the required height and width, filling the groove and shaping the bead while controlling heat input to minimize distortion and defects. The final cap pass shapes the top surface, smooths the contour, and seals the weld so it looks good and resists corrosion or environmental exposure. This order matters because without adequate root penetration the joint isn’t fully welded; without fill the weld can be underfilled; and without a dedicated cap pass the surface finish and contour would be poor.